Alternating-current generator.



No. 884,831. PATENTED APR. 14', 1908.

CL A. LOHR.

ALTERNATING CURRENT GENERATOR.

APPLIOATION FILED I'EB. 2, 1906.

IN VBN TOR A TTORNEYS UNITED STATES PATENT OFFICE.

CARL A. LOHB, OF WILKINSBURG, PENNSYLVANIA.

ALTEBNATING-CURRENT GENERATOR.

To all whom it may concern:

Be it known that-I, CARL A. Lona, a citizen of the Empire of Germanresiding in Wilkinsburg, in the county of llegheny and State ofPennsylvania, have invented certain new and useful Improvements inAlternating-Current Generators, of which the following is aspecification.

lhe invention herein described relates to alternating-current generatorswhich are intended mainly for the direct coupling with high-speed rimemovers, such as steamturbines. vi ith a frequency of 25 cycles er secondfor instance, the highest availa le speed which can be used inalternating-cur rent generators of the ordinary construction is limitedto 1500 revolutions per minute, while with a generator of theconstruction herein described the generator and primemover can be run atexactly twice the s eed which, aside from a number of electricaadvantages, is of advantage mainly on account of the better utilizationof the steam-turbine. In addition to this my invention enables an oeration of the generator at the same speed w ich is used for ageneration of alternatingcurrents of a frequency of 25 cycles forinstance, for a generation of alternating-currents of a higherfrequency, or generally speaking, my generator may be alternatelyswitched over from one alternating-current line to another of differentfrequency.

My invention will be best understood by reference to the accom anyindrawing Figures 1 and 2. Each these gures contams a part of myinvention, but for a given case onv one of the arrangements as shown inthe figures of the drawing will give the most advantageous desi n. Thearrangementsshown in the two figures of the drawing differ only in thata transformer is inserted in the conductors leading to the rotor in thearrangement shown in F1 2.

Similar letters of reference indicate the same parts in the differentfigures of the drawin In Fig. 1 of the drawing A represents the statorof an alternating-current generator and B the rotor of the same. Bothparts, stator and rotor, have alternating-current windin s which areshown in the drawing as three-p ase windin s.

The windings of t e stator A are connected b the triplepole double throwswitch 0, when thrown as shown by the full drawn position of thisswitch, by the conductors D Specification of Letters Patent.

Application filed February Patented April 14, 190B.

2, 1906. Serial N0- 299,115.

and E with an alternating-current line F. Furthermore the windings ofthe stator A can be connected, when swltch C is thrown as shown by thedotted position,-by means of the conductors D and G with anotheralternating-current line II. The alternatin -current lines F' and H aresystems of di erent frequency. The windings of the rotor B can beconnected over the collector-rings I, the brushes K, the conductors L,the trlple-pole double-throw switch M, when thrown as shown b the dottedposition, and the conductors N with the resistances or short-circuitingconductors 0. Also the windings of the rotor B can be connected when theswitch M is thrown as shown by the full drawn position over thecollector-rings I, brushes K, conductors L, switch M, conductors P,regulating resistances Q, and the conductors R with thealternating-current line F. The switches C and M are simultaneouslyoperated and may be mechanically connected as indicated by the line S inthe drawing. Thus it will be seen that by a single switch-throw mygenerator may be connected alternately with stator and rotor to .theline F, or only with the stator to the line H, the rotor being thenclosed u on itself. When the switches C and M are t rown as shown intheir dotted positions, the generator will act as asynchronousinduction-generator to the line H, and when the switches C and M arethrown as shown in their full drawn position, the generator will act assynchronous inductiongenerator to the line F. In order to secure asuccessful operation of this generator with both alternating-currentlines H and F, the fre uency of the line F must be over one half of t efrequency of the line H.

current line F be cycles per second, which frequency will be largelyused in the near future for alternating-current railway work, the numberof poles of the generators be two, as shown in the drawing, and theswitches C and M be thrown as shown in the full drawn position, theenerator will supply electric energy to the ine F when driven at a s eedof 1800 rotations per minute. With t e same speed, when the switches Cand M are thrown as shown in the dotted position, so as to connect thestator A with the lineH and so as to close the rotor B upon itself, thegenerator will supply electric energy to the line H, when the frequencyof this line is such as to produce in the stator A a mag- Suppose thefrequency of the alternatingdescribed must be excited byalternatingcurrents of the groper frequency. Thus m generator hereescribed is particularly we I suited to act as additional generator to asystem of two alternating-current lines and may be easily switched overfrom one line to the 'other by a single switch-throw, without changingthe speed of the rime-mover.

' which it supplies.

a the synchronous (double-connected) A special case in whic 1 thealternatin working on lines of differentfrequenc is o importance may beillustrated in the ollowing example: Supposing a power-station comprisesa group of alternating-current generators which supply a line of 15cycles per second for railway work, and a second grou of alternatincurrent generators, whic 1 supply a line 0 a frequency about between 25and 30 cycles per second for supplying incandescent lamps, which asknown cannot be satisfactorily operated with a frequency below 20 cyclesper second. The generators of the ordinary construction could not underretention of the same s eed as reuired by the prime-mover, be shiftedonto a line of different fre uency, and it is therefore necessary thateit er grou of generators must be sufiicient for the fu load of the lineEx erience has shown that the maximum loa s of two such lines are neverreached at the same time, and it is therefore readily discernible thatone or more generators may be dispensed with when generators of myimproved system are used, as the same permit, without change of s eed,the alternating working to that'line which is carrying the heavier load.My generator of t e works best to a line of lower frequency, while as agenerator of the asynchronous (singleconnected) t e to a line of higherfrequency.

In Fig. 2 have shown the same arrangement as in Fig. 1, with the onlyaddition of a transformer V, in case a lower volta e is desired for therotor, when connecte to the line F, or what is more im ortant, in case alower resistance is require when the rotor is acting as short-circuitedmember, the stator then being connected to the line H.

The re ulating resistances Q serve to equalize t e rotary fields in thestator and rotor when both members are connected to thealternating-current line F. The purpose of these regulating resistancesis to avoid cross-currents flowing between the windings of stator androtor. The connection of the rotor over a transformer would reresult ina lower resistance of the rotor windings and therefore require a lessslip over synchronism for a given output as asynchronousinduction-generator. The arrangement with or without a transformer inthe connections to the rotor has therefore an influence on the ratio offrequencies of the two alternating current lines.

In the case mentioned, having a generator-speed of 1800 rotations perminute and a frequency of 15 cycles er second in the alternating-currentline the frequency of the alternating-current line H must be less than30 cycles per second. If the frequency of this line be 25 cycles persecond, the rotorresistance must be higher, if the frequency of thisline be 29 or almost 30 cycles s., the rotor-resistance must be lower inor er to secure a satisfactory working of the generator to bothalternating-current lines, and especially in order to secure a desiredoutput of the generator when supplying the line H. Thus it will be seenthat in the combination as described and shown in the drawing thetransformer V is necessary for certain conditions and therefore forms apart of my invention.

The general princi 1e of my invention may be illustrated by the ollowingtwo examples:

Example 1. The generator consists similarly as an induction-motor whoserotor is provided with phase-windings and collector.-

rings of a rotary part (rotor), which is con-- nected either directly orover a transformer with an alternating-current line, and of a stationarypart (stator), which is also provided with alternating-current windings,and which is also connected with said alternatingcurrent line. With thisarrangement the magnetic alternating of rotary field which is producedin the rotor exerts, in connection with the mechanical rotation of therotor, an inducing effect on the windings of the stator,

while the alternating or rotary field which is induced in the stator hasin return an inducing effect on the windings of the rotor. In thisspecial case therefore, the generator acts as a synchronous generatorand represents the double-connected type of my generator.

Example 2. The rotor of the generator just described is switched out ofthe alternating-current line and its windings switched over thecollector-rings into a resistance or short-circuited. The stator of thegenerator may be connected to the same line or it may be connected witha line of different freuency. With this arrangement the mac ine operatesas asynchronous generator and represents the slngle-connected type of mygenerator.

As explained in the foregoing description, a main object of the presentinvention is an alternating-current generator, which can be readilyswitched over from one alternatingcurrent line to another of differentfrequency, without changing the s d of the generator or its prime-mover.fi y generator can be 40 in h rotary part, but malnly for obtainingknown by which such a motor can be started.

parts.

used in this manner in every case with alternating-current lines, thefrequencies of which are in such relation to each other, that thefrequency of the one line is somewhat more than one half of thefrequency of the other line. The synchronous operation of the generatorhas to be applied when supplying the line of lower frequency, and theasynchronous operation, when supplying the line of higher frequency.

In the following table I have given the speed of the generator for atwoole construction and a few frequency-com inations which can bealternately obtained, without changing the speed of the generator.

I do not desire to limit my inventlon to the application of twooppositelyerotating magnetic fields in stator and rotor of a generator,as this idea has been used heretofore for motors, where it could not-beapplied with any practical success, as such motor is synchronous and asno electrical means are The present invention employs this principle inExample 1, but enlarged and arranged in such a manner as to producespecial electrical and magnetic functions.

As previously explained an essential addition for certain cases istherefore: a transformer, inserted in the connections to the rotor, notonly for obviating too high tensions the short-circuiting of the rotor,or more pre-- cisely expressed, for obtaining a certain resistance ofthe rotor-windings and therefore a satisfactory running of the machineas asynchronous generator to an alternating current line of otherfrequency. Furthermore in a parallel connection of stator and rotor whensupplying the line F, an essential addition is; a device for regulatingthe strength of the magnetic field of one member of the generator, whichis represented in the drawing in the regulating resistances Q.

It is obvious that the machine can be runin every case in which it isoperated as a gene'rator, also as a motor, without making any changes inthe switch-device or in other Only in the. case in which the machine isrun as a" double-connected motor, the regulating resistances in thecircuit of the rotorhave the additional purpose, viz. to I the motorwithout external means,

speed up y electrical means, to the higher purely stated in theapplication filed by me on Sep-- tember 7, 1905, Serial No. 277,336.

While I- desire to extend all the claims which I make for the generatorto the machine when running as a motor as this will be readilyunderstood by any one skilled in the art, I desire to confine myself inthis application and in the claims, to a generator, inasmuch as thespecial arrangement as motor is described in my pending application Ser.No.

277,336, of September 7, 1905, I- beg to state, however, that theinvention herein described consists not only in a simple revers ing ofthe motor so as to use it as a generator, but as will appear from thedescription and drawing, in the combination with two alternating currentlines, in a manner which is applicable to a generator, but generally fora motor outof the scope of apphcation.

Having thus described my invention, I claim as new and desire to secureby Letters Patent- 1. In combination, with two alternatin current linesof different frequency and an 25 ternating-current generator havingalternate ing-current windings on both of its members, means foralternately connecting at will the windings of both membersof saldgenerator to one of said alternating-currentlines, or the winding of onemember of said generator to the other of said alternatin -current lineshaving the winding of the ot er member of said generator closed uponitself.

2. In combination, with two alternatin current lines of differentfrequency and an a ternating-current generator having alternat-'generator directly and the other member of said generator over atransformer with the one of said alternating-current'lines, means.

for connecting said one member of said alterhating-current generatorwith the other of said' alternating-current lines and closing said othermember upon itself, the secondary winding of said transformer and thewinding of said other member being designed so as to produce with thesame enerator-speed the same or approximately t e same amount ofelectrical ener y, when said enerator is switched over 0m one line to te other, all substantially as described.

In testimony, that I claim the foregoing as my invention, I have signedmy name in presence of two subscribin witnesses.

v CA L A. LOHR. Witnesses:

' HANS WEICHSEL, R. L. HoFFMAm

